植被混凝土生态修复技术是当前国内用于裸露陡边坡植被恢复的典型技术之一，具备肥力持续供给能力是植被混凝土有别于其他建筑材料的基本属性。冻融循环作用下物理结构剧变导致养分固持能力减弱是限制植被混凝土在高寒地区应用的关键因素，但养分固持能力变化的深层原因尚不清楚。通过控制性试验，以初始含水率和冻融循环频次为变量，测定了植被混凝土水稳性团聚体粒径分布、团聚特征参数、主要养分含量及其淋溶流失率的变化规律。结果表明：随初始含水率提高，植被混凝土中水稳性微团聚体向大团聚体转化，尤其以≥1~2 mm粒组增幅最多，团聚特征参数变化也反映出团聚体稳定性随之提高；冻融循环导致水稳性团聚体平均粒径不断减小，但会随冻融频次增长逐步趋于稳定。初始含水率的提高促使各养分含量略有增加；冻融循环作用下有机质、铵态氮、有效磷、速效钾含量仍有增长，但硝态氮含量不断降低。同时，冻融循环还会导致各养分淋溶流失率不断增大，最大增幅可超过90%，并随冻融频次增长趋于稳定。这说明冻融循环对养分固持能力的影响会逐步减弱，而且侧面反映出团聚结构与养分固持能力间存在紧密联系。Pearson相关性分析进一步表明，团聚特征参数与各养分淋溶流失率均达到显著相关水平，综合考虑显著性水平与相关性系数绝对值，认为团聚特征参数中几何平均直径与各养分淋失率相关程度最高，最适合用于表征植被混凝土的养分固持能力。上述研究结果证实，冻融循环作用下团聚效应减弱是导致植被混凝土养分固持能力降低的深层原因。

Vegetation concrete （VC） ecological protection technology is an effective solution for the vegetation recovery of bare steep slopes， which has been increasingly applied in cold regions in recent years. When the technology is implemented， the nutrient retention ability of VC substrate is essentially concerned. Under the actions of freeze-thaw cycles， fertility of the VC substrate as well as natural soil is thought to degrade gradually. It has been recognized that the nutrient retention ability of soil is significantly correlated with its physical structure. Similarly， the nutrient retention ability of VC substrate could be supposed to be physical structure-dependent. To enhance the comprehensive performance of VC substrate in cold regions， the investigation of nutrient retention ability is required， which nevertheless is still little identified. In this study， a series of freeze-thaw cycle experiments for VC substrate were conducted， and the effects of initial water contents and freeze-thaw cycles on characteristic parameters of water-stable aggregates and leaching loss rates of major nutrient substances were studied. A freeze-thaw cycle for specimen treatment， performed by a fast air freeze-thaw test machine， was defined as the freezing process of 12 hours at -20 ℃ in addition to the thawing process of 12 hours at +20 ℃. Except for the non-treatment， namely without freeze-thaw cycle， 7 treatments were considered to prepare the specimens， including 1 cycle， 2 cycles， 4 cycles， 8 cycles， 16 cycles， 32 cycles and 64 cycles. According to the field experience in practice， the lower and upper initial water contents of specimens were designated to be 18% and 24%， respectively. The results showed that the water-stable aggregates of the VC substrate were mainly composed of the particles with size ranging from 0.05 mm to 0.25 mm， which contained the proportions over 50% of total mass for all specimens. With increasing initial water content， the water-stable micro-aggregates transformed into the macro-aggregates， among which the particles of ≥1~2 mm were found to hold the maximum increase rate in proportion. Other parameters， which could quantitatively represent the characteristics of aggregate structure， also showed that the aggregate stability increased with initial water content. In addition， the contents of particles smaller than 0.25 mm were positively related to freeze-thaw cycles， while that of the particles larger than 0.25 mm showed the inverse trend. This indicated that the average value of aggregate particle sizes decreased with freeze-thaw cycles. It was noticed that the dispersion rates of aggregate increased with initial water content， which showed that destructive action to aggregate caused by freeze-thaw cycles was greater than the reinforcement provided by the increasing cement hydration products. Furthermore， the freeze-thaw cycles required for the aggregate characteristic parameters of VC to reach the stable state were more than that for natural soil. It may be due to that natural soil would go through the repetitive process of decomposition and aggregation， while destruction process of cement hydration products was irreversible. For the fertility， a high initial water content was associated with the increasing contents of major nutrient substances. Contents of organic matter， ammonium nitrogen （NH₄⁺-N）， available phosphorus （PO₄^3--P） and potassium （K⁺） still increased with freeze-thaw cycles， while content of nitrate nitrogen （NO₃^--N） decreased. Moreover， the leaching losses of these nutrient substances increased with freeze-thaw cycles obviously. From the Pearson correlation analysis， the leaching loss rates of major nutrient substances were found to correlate closely with the aggregate characteristic parameters. In consideration of significance levels and absolute values of correlation coefficients， geometric mean diameter （GMD） could be suggested as the reasonable index to describe the nutrient retention ability of VC substrate. The results may contribute to illustrate the underlying reason for VC substrate fertility degradation under freeze-thaw cycles and provide theory basis for countermeasure.

融雪期的侵蚀外营力主要以冻融和融雪径流为主,该营力可能会影响土壤结构和团聚体稳定性,从而对融雪侵蚀过程产生影响。在融雪期,融雪径流过程会导致团聚体输移破碎,但是关于冻融对团聚体输移破碎的影响研究鲜有报道。本研究以东北典型黑土区5～7和3～5 mm团聚体为对象,分析了不同冻融次数(0、1、5、10、15和20次)下水稳性团聚体组成、平均重量直径(MWD)、标准化平均重量直径(NMWD)和不同冻融次数、不同输移距离(5、10、15、20、25和30 m)下团聚体输移破碎率(BR)及冻融和输移共同作用对BR的贡献度(CT),研究融雪期典型黑土团聚体输移破碎特征。结果表明: 5～7和3～5 mm团聚体冻融循环后主要以0.5～1 mm粒径为主,随着冻融次数增加其MWD值总体呈下降趋势,并且在相同冻融次数下3～5 mm团聚体NMWD大于5～7 mm。5～7和3～5 mm团聚体随着输移距离的增加BR逐渐增加,尤其是在1次冻融条件下,与未冻融组相比输移距离为5、10、15、20、25和30 m时BR分别显著增加59.7%、32.2%、13.7%、6.2%、13.4%、7.5%和60.0%、39.0%、18.4%、13.0%、6.3%、6.1%;但随着冻融次数的增加,BR增加相对缓慢。团聚体输移破碎主要受输移距离(CT=54.6%)和冻融循环(CT=26.2%)的影响,并且冻融循环主要改变团聚体稳定性,进而影响团聚体输移破碎率。可见,在融雪期,冻融循环降低了土壤团聚体稳定性,致使融雪径流过程中团聚体输移破碎严重,土壤更易随水流迁移引发水土流失,因此,应重视该时期的土壤侵蚀及其防治。

During the snowmelt period, the external erosive forces are dominated by freeze-thaw cycles and snowmelt runoff. These forces may affect soil structure and aggregate stability, thereby influencing snowmelt erosion. The process of snowmelt runoff can lead to the breakdown of aggregates during their transportation. However, few studies examined the effects of freeze-thaw cycles on the breakdown of aggregates during transportation. Focusing on 5-7 and 3-5 mm soil aggregates of typical black soil region in Northeast China, we analyzed the composition of water-stable aggregates, mean weight diameter (MWD), normalized mean weight diameter (NMWD), as well as breakdown rate of soil aggregates (BR) under different freeze-thaw cycles (0, 1, 5, 10, 15 and 20 times) and different transport distances (5, 10, 15, 20, 25 and 30 m). We further investigated the contribution (CT) of both freeze-thaw cycles and transport distances to BR. The results showed that: 1) After freeze-thaw cycles, the 5-7 and 3-5 mm aggregates were mainly composed of particles with a diameter of 0.5-1 mm. With increasing frequency of freeze-thaw cycles, the MWD generally showed a downward trend. Moreover, under the same number of freeze-thaw cycles, the NMWD of 3-5 mm aggregates was higher than that of 5-7 mm aggregates. 2) As the transport distance increased, the BR of 5-7and 3-5 mm aggregates gradually increased. Compared that under control group, the BR under one freeze-thaw cycle increased by 59.7%, 32.2%, 13.7%, 6.2%, 13.4%, 7.5%, and 60.0%, 39.0%, 18.4%, 13.0%, 6.3%, 6.1% at the condition of 5, 10, 15, 20, 25 and 30 m transport distances, respectively. However, with increasing frequency of freeze-thaw cycles, the BR increased slowly. 3) The breakdown of soil aggregates was mainly influenced by the transport distance (CT=54.6%) and freeze-thaw cycles (CT=26.2%). Freeze-thaw cycles primarily altered the stability of soil aggregates, which in turn affected the BR. Therefore, during the snowmelt period, freeze-thaw cycles reduced the stability of soil aggregates, leading to severe breakdown of soil aggregates during snowmelt runoff process. This made the soil more susceptible to migration with snowmelt runoff, which triggered soil erosion. Therefore, more attention should be paid on the prevention of soil erosion during snowmelt period.

Biochar can improve soil health and fix CO2 by altering soil microenvironment, thus impacting the global carbon cycle and the change of soil ecological environment. Recent studies show that cotton byproduct-derived biochar is a potential effective amendment for soil improvement so that it could play an important role in agricultural and environmental conservation. In this work, research topics on cotton byproduct-derived biochar in soil in last decade and so are systematically reviewed for better understanding of the progresses of cotton byproduct-derived biochar in (i) the morphologic and physicochemical characterization, (ii) latest research hotspots and trends, (iii) the roles in soil reclamation, and (iv) relevant carbon sequestration mechanisms. Finally, the future research directions regarding cotton byproduct-derived biochar mingled to soil environment are discussed. Insight derived from this work would provide scientific basis for promoting more applications of cotton byproduct-derived biochar in soil ecological restoration and carbon fixation.

为研究水盐运移情况下硫酸盐渍土盐-冻胀规律,采用室内土柱冻融试验,利用teros-12传感器及位移计测定冻融循环过程中土体含水率、电导率、温度和位移的变化,分析了水盐运移规律及其对土体盐-冻胀变形的影响。试验结果表明:在自上而下的冻结方式中,土体底部水分向冻结锋面移动,带动盐分向上聚积,同时土体体积含水率和电导率随温度的升降循环存在明显“滞回”现象。冻结阶段土体发生膨胀,竖向变形可分为3个阶段:①调整阶段,由生成芒硝引起;②快速变形阶段,由生成芒硝与冰晶共同作用所致;③缓慢变形阶段,由生成少量冰晶所致。融化阶段土体竖向变形以一定融陷速率发生快速融沉。含硫酸钠盐渍土冻融循环过程中,竖向变形随时间的变化关系呈现“桃尖型”趋势,且每次冻融土体竖向变形速率基本一致。随冻融次数的增加,盐-冻胀率也不断增加。土体含盐量越高对土体竖向变形的影响越显著。本研究可为揭示含硫酸盐渍土盐分和水分随温度变化的“滞回”现象以及水-盐-热-力耦合模型的建立提供数据支撑。

The regularities of water and salt migration in sulfate saline soil as well as their impacts on the frost heave of soil were investigated via indoor soil column test. The changes in moisture content, electrical conductivity, temperature, and displacement during the freeze-thaw cycles were measured by teros-12 and displacement meter. The experimental results demonstrated that in the freezing process from top to bottom, the bottom water moved toward the freezing front, driving the salt accumulating upwards. Meanwhile, the cycles of temperature rising and falling generated a notable hysteresis effect on volumetric moisture content and electrical conductivity of soil. The soil swelled during freezing, and the vertical deformation can be divided into three stages: the adjustment stage caused by the formation of mirabilite; the rapid deformation stage induced by the combined action of mirabilite and ice crystal; the gradual deformation stage resulted from a small amount of ice crystals. During melting, the vertical deformation of soil mass underwent swift melting at a certain melting rate. For saline soil containing sodium sulfate, the curve of vertical deformation during freeze-thaw cycles against time presented a peach-shaped trend, and the vertical deformation rate of each cycle was basically consistent. The salt frost heaving rate increased with the proceeding of freezing and thawing. Higher salt content had more evident impact on vertical deformation. The research findings offer data support for revealing the hysteresis effect and also for the establishment of water-salt-thermo-mechanics coupling model.

【目的】沿海城市轨道交通主要穿越海相深厚软土,需要大量使用冻结法施工,而该地区典型土层热物理特性是冻结法设计的关键依据。研究土质、冻融条件等因素对海相人工冻土冻结温度、热物理性质和冻融性质的影响可为该地质条件下的隧道施工提供基础资料。【方法】选取宁波地区3种典型土层,即淤泥质黏土、粉质黏土和砂质粉土,开展冻结温度和热物理参数测定,以及封闭与开放系统下冻胀融沉试验。【结果】3种土层冻结温度为-0.43～-0.23 ℃,且以砂质粉土的较高,粉质黏土的次之,淤泥质黏土的较低; 不同土层热物理性质不同,但其常温土的导热系数和容积热容量大小呈现一致性,表现为砂质粉土最大,粉质黏土次之,淤泥质黏土最小; 冻土的导热系数、容积热容量和导温系数均大于常温土,冻土导热系数为常温土导热系数的1.37～1.77倍,且颗粒越粗差异越大; 各土层冻胀率和融沉系数相差较大,冻胀率较大的土层其融沉系数也较大,表现为淤泥质黏土＞粉质黏土＞砂质粉土; 开放系统补水冻结过程下各土层冻胀率和融沉系数分别为封闭系统冻结过程不补水工况下冻胀率和融沉系数的1.23～1.88倍和1.21～1.84倍。不论是开放系统还是封闭系统,海相土体各土层的融沉过程相似,可分为缓慢融沉、快速融沉和稳定融沉3个阶段。【结论】海相土体的冻结温度、热物理性质和冻融性质与其土质、状态和冻融条件等因素密切相关,在进行海相土体冻结法设计与施工时,应充分考虑其物理特性的差异性。

Using observational data from Zoige Station in the east of the Tibetan Plateau and the land surface process model, Community Land Model version 3.5 (CLM3.5), a degradation experiment, in which the freezing and thawing process of the model had been removed, was designed, then a simulation experiment for one year was conducted. Through comparison of the results between the original simulation and the sensitive experiment, the role of freezing and thawing process in the change of soil temperature and distribution of energy flux was preliminary analyzed. The conclusions are as follows:(1) Freezing and thawing process is a "buffer" for the change of soil temperature. Releasing the phase change energy to the environment during freeze slows the cooling rate of soil, which also makes the soil temperature not too low; while absorbing the phase change energy from the environment during the thaw slows the heating rate of soil. (2) Freezing and thawing process changes the surface radiation. The freeze of soil changes surface albedo, which changes the upward shortwave radiation. Due to the buffer role of freezing and thawing process, which delays the decrease of soil surface temperature, the upward longwave radiation is changed actually, which leads to variation of net radiation. (3) Freezing and thawing process remarkably changes the distribution of land surface energy. The release and absorption of phase change energy changes the transportation of energy between land and atmosphere, which also changes the sensible heat flux and latent heat flux by changing the surface temperature and surface evaporation. During the freezing process and the complete freezing phase, the sensible and latent heat flux increases, but the heat and latent heat flux decreases during the thawing process. The influence of freezing and thawing process on soil heat flux and sensible heat flux is more significant during the freezing process and the complete freezing phase, while that on latent heat flux is more significant during the thawing process.

Biochar addition can improve the physical and hydraulic characteristics of sandy soil. This study investigated the effects of biochar on water holding capacity and water movement in sandy soil under drip irrigation. By indoor simulation experiments, the effects of biochar application at five levels (0%, 1%, 2%, 4%and 6%) on the soil water retention curve, infiltration characteristics of drip irrigation and water distribution were tested and analyzed. The results showed thatbiochar addition rate was positively correlated with water holding capacity of sandy soil and soil available water. Within the same infiltration time, with an increasing amount of added biochar, the diffusion distance of the horizontal wetting front (HWF) tended to decrease, but the infiltration distance of vertical wetting front (VWF) initially declined and then rose. The features of wetted bodies changed from "broad-shallow" to "narrow-deep" type. The relationship between the transport distance of HWF and VWF and the infiltration time was described by a power function. At the same distance from the point source, the larger was the amount of added biochar, the higher was the soil water content. Biochar had a great influence on the water content of the layer with biochar (0-200mm) and had some effects at 200-250mm without biochar; but had less influence on the soil water content deeper than 250mm. For the application rate of biochar of 4%, most water was retained within 0-250mm soil layer. However, when biochar application amount was high (6%), it would be helpful for water infiltration. During the improvement of sandy soil, biochar application rate of 4% in the plow layer had the best effect.